Nucleophosmin/B23 is a nucleolar phosphoprotein 20 times more abundant in tumor or proliferating cells than in normal or resting cells. Its putative function is assembly and/or transport of ribosomes. When tumor cells are treated with some anticancer drugs, the protein temporarily translocates from the nucleolus to the nucleoplasm. It is concluded these drugs affect the protein's binding site or transport and cause translocation. The proposed studies are designed to use the increased synthesis of nucleophosmin/B23 in cancer cells as a target for new anti- cancer drug development and to understand its role in tumor cell proliferation.The specific aims are l) to determine the drug binding site in human leukemic cells 2)to inhibit the growth of human leukemic cells (K562) by antisense RNA/DNA 3)to understand the structure and function of nucleophosmin/B23 and its relationship with carcinogenesis and 4) to determine and characterize the human genomic DNA sequences of nucleophosmin/B23.